1. Field of the Invention
This invention relates to luminescent compositions. More particularly it relates to a titanium-activated lanthanum oxysulfide and to a process for preparing same.
2. Prior Art
Phosphors having a lanthanum oxysulfide host are known. Rare earth activators have in the past been used to activate the lanthanum oxysulfide host. For example, U.S. Pat. No. 2,462,547 discloses europium and samarium as activators for lanthanum oxysulfide to form a phosphor for emitting light when excited by ultraviolet light. U.S. Pat. No. 3,418,247 indicates that dysprosium, erbium, europium, holmium, neodymium, praseodymium, samarium, terbium, or thulium can be used as activators for lanthanum oxysulfide to form a cathodoluminescent phosphor. U.S. Pat. No. 3,725,704 indicates that a terbium-activated lanthanum oxysulfide is an efficient x-ray phosphor. All of the foregoing art indicates that rare-earths are useful as activators for lanthanum oxysulfide. No art has been found that indicates that non-rare earth metals are useful as activators. Since many non-rare earth metals are more common than rare earths, it is believed a phosphor composition which employs titanium as an activator offers an attractive alternate activator and is thus an advancement in the art.